Claiming Benefit of Prior Filed Application
Background
[0002] The disclosure relates to porous honeycomb ceramics and methods of making, and more
particularly to porous cordierite honeycomb ceramics useful in catalytic converters
and particulate filters, such as for engine exhaust after-treatment.
Summary
[0003] The disclosure provides a high-porosity cordierite honeycomb substrate or diesel
particulate filters having fine pore size which substrates or filters have little
or no microcracking and can maintain a high thermal shock resistance even with an
increased coefficient of thermal expansion that is expected in the absence of microcracking.
[0004] The disclosure provides honeycomb bodies that have improved strength that makes them
excellent choices for the fabrication of catalytic converter substrates or diesel
particulate filters (DPFs) having very thin walls, together with, if desired, low
cell densities for reduced back pressure and reduced thermal mass (faster light-off).
The improved strength can also enable the manufacture of ceramic bodies having higher
porosities for use in converter substrates and DPFs for further reduction in thermal
mass or for storage of high amounts of catalyst (such as for SCR or 4-way catalyzed
DPFs) while maintaining adequate strength. The fine median pore size of the inventive
honeycomb bodies promotes high strength, and can additionally provide high filtration
efficiency in DPFs, yielding articles having improved filtration of very fine particles
during the early stages of soot deposition.
[0005] In embodiments, the porous ceramic honeycomb bodies generally comprise a primary
cordierite ceramic phase and have a porosity %P of at least 50%; a median pore size
diameter d
50 less than 10.0 microns; a thermal shock parameter (TSP) of at least 450°C; and an
elastic modulus E-ratio, E
900°C/E
25°C, of not more than 1.01. Thermal shock parameter TSP is defined as (MOR
25°C/E
25°C)(CTE
500-900°C)
-1, MOR
25°C is the four-point modulus of rupture strength at 25°C, E
25°C is the Young's elastic modulus at 25°C, E
900°C is the elastic modulus measured at 900°C during heating, and CTE
500-900°C is a high temperature thermal expansion coefficient at 500°C to 900°C.
[0006] In embodiments, the disclosure also provides a method for making the porous ceramic
honeycomb structures described herein. The method generally comprises mixing inorganic
raw materials, an organic binder, and a liquid vehicle to form a plasticized batch,
forming a green body from the plasticized batch, drying the green body, and firing
the body to provide the cordierite ceramic structure.
[0007] Additional embodiments of the disclosure will be set forth, in part, in the detailed
description, and any claims which follow, or can be learned by practice of the disclosure.
The foregoing general description and the following detailed description are exemplary
and explanatory only and are not restrictive.
Brief Description of the Drawings
[0008] The accompanying drawings illustrate certain embodiments of the disclosure.
[0009] FIG. 1 is a plot of the elastic modulus (psi) versus temperature (°C) during heating
and cooling of an inventive low microcracked cordierite honeycomb body.
[0010] FIG. 2 is a plot of the elastic modulus (psi) versus temperature (°C) during heating
and cooling of a highly microcracked cordierite ceramic body..
[0011] FIG. 3 is an isometric view of porous honeycomb substrate.
[0012] FIG. 4 is an isometric view of porous honeycomb filter.
[0013] FIG. 5 is a plot of strain tolerance, (MOR/E)
25°C, versus the % porosity for inventive low microcracked cordierite embodiments of the
disclosure (filled circles) and an inferior example having low (MOR
25°C/E
25°C) and intermediate porosity (open circle).
Detailed Description
[0014] Various embodiments of the disclosure will be described in detail with reference
to drawings, if any. Reference to various embodiments does not limit the scope of
the disclosure, which is limited only by the scope of the claims attached hereto.
Additionally, any examples set forth in this specification are not limiting and merely
set forth some of the many possible embodiments for the claimed invention.
[0015] Disclosed are materials, compounds, compositions, and components that can be used
for, can be used in conjunction with, can be used in preparation for, or are products
of the disclosed method and compositions. These and other materials are disclosed
herein, and when combinations, subsets, interactions, groups, etc. of these materials
are disclosed that while specific reference of each various individual and collective
combinations and permutation of these compounds may not be explicitly disclosed, each
is specifically contemplated and described herein. Thus, if a class of substituents
A, B, and C are disclosed as well as a class of substituents D, E, and F and an example
of a combination embodiment, A-D is disclosed, then each is individually and collectively
contemplated. Thus, in this example, each of the combinations A-E, A-F, B-D, B-E,
B-F, C-D, C-E, and C-F are specifically contemplated and should be considered disclosed
from disclosure of A, B, and C; D, E, and F; and the example combination A-D. Likewise,
any subset or combination of these is also specifically contemplated and disclosed.
Thus, for example, the subgroup of A-E, B-F, and C-E are specifically contemplated
and should be considered disclosed from disclosure of A, B, and C; D, E, and F; and
the example combination A-D. This concept applies to all embodiments of this disclosure
including any components of the compositions and steps in methods of making and using
the disclosed compositions. Thus, if there are a variety of additional steps that
can be performed each of these additional steps can be performed with any specific
embodiment or combination of embodiments of the disclosed methods, and that each such
combination is specifically contemplated and should be considered disclosed.
[0016] Porous cordierite ceramic honeycomb structures having high thermal shock resistance
and a fine pore size are useful for pollution control devices such as catalytic converter
substrates, SCR substrates, and certain diesel particulate filters (DPFs). In these
applications, porosity in the substrate provides a means to "anchor" the washcoat
or catalyst onto the surface, or within the interior, of the channel walls, and serves
to filter fine particulates from the exhaust gas in the case of DPFs. Historically,
high thermal shock resistance in cordierite honeycomb ceramics has been achieved by
maintaining a low coefficient of thermal expansion (CTE) which, in turn, is attained
through microcracking and textural orientation of the cordierite crystals with their
negative thermal expansion z-axes (also referred to as c-axes) oriented within the
plane of the wall of the honeycomb. In a further effort to maintain a low coefficient
of thermal expansion, previous approaches have also emphasized the use of high-purity
raw materials low in sodium, potassium, calcium, iron, etc., in order to minimize
the presence of secondary phases, especially a glass phase.
[0017] Recent trends in exhaust after-treatment for gasoline engines have placed greater
demands on the catalytic converters. Specifically, converters with lower mass per
unit volume are desired because such converters will heat up faster and begin catalytic
conversion of the exhaust sooner, thereby resulting in lower overall emission of pollutants
during a driving cycle. Lower mass can be achieved by any combination of lower cell
density, thinner walls, or higher porosity, all of which may reduce the strength of
the converter substrate. Achieving high strength in low-mass cordierite honeycombs
remains a challenge because the presence of microcracks, which are necessary for very
low CTE, may also reduce the strength of the ceramic. In DPFs, higher porosity is
also often desired in cases where the DPF is catalyzed. This higher porosity similarly
may lower the strength of the DPF.
[0018] A second challenge faced by catalyzed substrates or DPFs comprised of a microcracked
cordierite ceramic is penetration of very fine catalyst washcoat particles into the
microcracks within the cordierite matrix, or precipitation of dissolved components
from the washcoat and catalyst system in the microcracks. In DPFs, it is also possible
for ash or soot particles to enter the microcracks. The presence of particles within
the microcracks may interfere with the closing of the microcracks during heating,
essentially pillaring the cracks open. This may result in an increase in the coefficient
of thermal expansion (CTE) and may also cause an increase in elastic modulus (E),
both factors which may contribute to a reduced thermal shock resistance.
[0019] Although previous efforts at improving thermal shock resistance have focused on reducing
the coefficient of thermal expansion, the thermal shock resistance of a ceramic material
can also be improved by increasing the ratio of the strength (such as measured by
the modulus of rupture) to Young's elastic modulus, MOR/E. The quantity MOR/E is also
known as the strain tolerance of the ceramic.
[0020] In embodiments, the disclosure provides a high-porosity cordierite honeycomb substrate
or DPF with fine pore size that exhibits little or no microcracking and maintains
a high thermal shock resistance even with an increase in the coefficient of thermal
expansion that occurs in the absence of microcracking. Such a substrate exhibits improved
strength, and also possesses a thermal shock resistance that is less sensitive to
the presence of the washcoat and catalyst.
[0021] "Include," "includes," or like terms means including but not limited to.
[0022] The singular forms "a," "an," and "the" include plural referents unless the context
clearly dictates otherwise. Thus, for example, reference to a "component" includes
embodiments having two or more such components, unless the context clearly indicates
otherwise.
[0023] "Optional" or "optionally" means that the subsequently described event or circumstance
can or cannot occur, and that the description includes instances where the event or
circumstance occurs and instances where it does not. For example, the phrase "optional
component" means that the component can or can not be present and that the disclosure
includes both embodiments including and excluding the component.
[0024] Ranges can be expressed herein as from "about" one particular value, to "about" another
particular value, or "about" both values. When such a range is expressed, another
embodiment includes from the one particular value, to another particular value, or
both. Similarly, when values are expressed as approximations, by use of the antecedent
"about," the particular value forms another embodiment. The endpoints of each of the
ranges are significant both in relation to the other endpoint, and independently of
the other endpoint.
[0025] "Weight percent," "wt. %," "percent by weight" or like terms referring to, for example,
a component, unless specifically stated to the contrary, refers to the ratio of the
weight of the component to the total weight of the composition in which the component
is included, expressed as a percentage.
[0026] In embodiments, the porous ceramic honeycomb bodies exhibit relatively high levels
of porosity. For example, the ceramic honeycomb bodies of the disclosure can have
a total porosity %P ≥ 45% such as a total porosity (%P) of the porous body of at least
45%, at least 50%,and at least 55%. Additionally or alternatively, the ceramic honeycomb
bodies of the disclosure can have a total porosity %P ≥ 52%, %P ≥ 55%, or even %P
≥ 58%. In embodiments, the ceramic honeycomb bodies of the disclosure can have a %P
≥ 60% or even %P ≥ 65%.
[0027] In embodiments, the high total porosity can preferably be comprised of a network
of interconnected pores having relatively fine pore sizes and a relatively narrow
pore size distribution. In embodiments, the fine pore size can be characterized by
a median pore diameter (d
50) that does not exceed 10 microns.
For example, the median pore diameter can be in the range of about 1-10 µm. In embodiments,
the median pore diameter d
50 can be less than about 8µm, less than 7 µm, less than 6 µm, less than 5 µm, or even
less than about 4 µm. In a preferred embodiment, the median pore diameter can be less
than about 7.9 µm.
[0028] A narrow pore size distribution can provide low soot-loaded pressure drop and can
enable high filtration efficiency when the body is used as a particulate filter. The
relative narrowness of the pore size distribution of the porosity of the porous body
of the disclosure can be characterized by a calculation of d
f or d
b, wherein d
f = (d
50-d
10)/d
50 and d
b = (d
90-d
10)/d
50. The parameters d
10, d
50, and d
90 in these equations are conventionally used and defined herein as the pore diameters
at which 10%, 50%, and 90%, respectively, of the pore volume of the material resides
in pores of smaller pore diameter, as measured by standard mercury porosimetry. Thus,
d
10 < d
50 < d
90 in these measurements. In embodiments, values for d
f can include, for example, d
f ≤ 0.55, d
f ≤ 0.50, d
f ≤ 0.45, d
f ≤ 0.40, d
f ≤ 0.37, d
f ≤ 0.35, and even d
f ≤ 0.30.
[0029] As noted above, the narrow pore size distribution can also be characterized by the
overall breadth of the pore size distribution as defined by the equation d
b = (d
90-d
10)/d
50. For example, values of d
b can include d
b ≤ 1.50, d
b ≤ 1.20, d
b ≤ 1.00, d
b ≤ 0.90, or even d
b ≤ 0.80.
[0030] The durability of the disclosed ceramic articles under thermal shock conditions can
also be characterized by the calculation of a thermal shock parameter (TSP). More
specifically, TSP is an indicator of the maximum temperature difference a body can
withstand without fracturing when the coolest region of the body is at about 500°C.
Thus, for example, a calculated TSP of about 450°C implies that the maximum temperature
at some position within the honeycomb body must not exceed 950°C when the coolest
temperature at some other location within the body is 500°C. The thermal shock parameter
is calculated according to the equation TSP = (MOR
25°C/E
25°C)(CTE
500-900°C)
-1 wherein MOR
25°C is the modulus of rupture strength at 25°C, E
25°C is the Young's elastic modulus at 25°C, and CTE
500-900°C is the mean thermal expansion coefficient from 500°C to 900°C.
[0031] The modulus of rupture, MOR, is measured by the four-point method on a cellular bar,
such as either about 0.5 x 1.0 x 5.0 inches or about 0.25 x 0.5 x 2.5 inches, whose
length is parallel to the channels of the honeycomb. The MOR is a measure of the flexural
strength of the honeycomb body. A high value of MOR is desired because this corresponds
to greater mechanical durability of the body and higher thermal durability and thermal
shock resistance. A high value of MOR also yields higher values for the thermal shock
parameter,
(MOR
25°C/E
25°C) (CTE
500-900°C)
-1.
[0032] The elastic modulus (Young's modulus), E, is measured by a sonic resonance technique
in which the specimen is a 0.5 x 1.0 x 5.0 inch bar and in which the length of the
bar is parallel to the length of the channels. The elastic modulus is a measure of
the rigidity of the body. A low value of E is desired because this corresponds to
greater flexibility of the body and higher thermal durability and thermal shock resistance.
A low value of E also yields higher values for the thermal shock parameter, (MOR
25°C/E
25°C)(CTE
500-900°C)
-1.
[0033] The coefficient of thermal expansion, CTE, is measured by dilatometry along the axial
direction of the specimen, which is the direction parallel to the lengths of the honeycomb
channels. As noted above, the value of CTE
500-900°C is the mean coefficient of thermal expansion from 500 to 900°C. Similarly, the value
of CTE
25-800°C is the mean coefficient of thermal expansion from 25 to 800°C, and the value of CTE
200-100°C is the mean coefficient of thermal expansion from 200 to 1000°C, all as measured
during heating of the sample. A low value of CTE is desired for high thermal durability
and thermal shock resistance. A low value of CTE yields higher values for the thermal
shock parameter, (MOR
25°C/E
25°C)(CTE
500-900°C)
-1. In embodiments, the CTE
500-900°C is preferably not more than 23x10
-1/°C, 22x10
-7/°C, 21x10
-7/°C, 20x10
-7/°C, and even not more than 19x10
-7/°C.
[0034] In embodiments of the disclosure, it is preferred that the thermal shock parameter
values of the honeycomb bodies be TSP ≥ 450°C, TSP ≥ 500°C, TSP ≥ 525°C, TSP ≥ 550°C,
and even TSP ≥ 600°C. In embodiments, the thermal shock parameter values can be TSP
≥ 700°C, TSP ≥ 800°C, and even TSP ≥ 900°C. From these exemplary TSP values in embodiments
of the disclosure, the Thermal Shock Limit (TSL) of ceramic honeycomb bodies can be
calculated. As noted above, the thermal shock limit is conventionally considered to
be the maximum temperature to which the center of the body can be heated when the
surface of the body is 500°C, without suffering cracking damage. TSL can be estimated
by adding 500°C to the value of Thermal Shock Parameter (TSP) as according to TSL
= TSP + 500°C.
[0035] In embodiments, a large proportion of highly interconnected pores have a narrow pore
size distribution of the cordierite honeycomb bodies and may contribute importantly
to the high strain tolerance and high TSP values obtained. High pore interconnectivity
in these low microcracked ceramics has the effect of reducing elastic modulus values
to a greater extent than MOR values. Thus, the ratio strain tolerance (MOR
25°c/E
25°c) also denoted (MOR/E)
25°C, upon which the TSP value depends, is favorably impacted by the amount of porosity
of these low microcracked ceramics (FIG. 5). In embodiments, a relatively high ratio
of (MOR/E)
25°C is provided, where (MOR/E)
25°C ≥ 0.10%, (MOR/E)
25°C ≥ 0.11 %, (MOR/E)
25°C ≥ 0.12%, (MOR/E)
25°C ≥ 0.13%, (MOR/E)
25°C ≥ 0.14%, (MOR/E)
25°C ≥ 0.15%, (MOR/E)
25°C ≥ 0.16%, or even (MOR/E)
25°C ≥ 0.17%.
[0036] In embodiments of the disclosure, the porous cordierite ceramic honeycomb contains
a rare earth metal oxide. The rare earth metal oxide is preferably present in an amount
from 0.25 to 4.0 weight percent of the ceramic body, and more preferably from 0.5
to 3.0 weight percent, and even more preferably from 0.7 to 2.0 weight percent. The
rare earth oxide is preferably yttrium or lanthanum oxide. It is further preferred
that the rare earth oxide be present, at least in part, in a glass phase within the
microstructure of the ceramic. It has been discovered that the presence of a rare
earth oxide serves to improve the strength of the body and to reduce microcracking.
[0037] The honeycomb bodies of the disclosure can possess a microstructure in which the
cordierite crystallites are randomly oriented or, alternatively, in which they are
preferentially oriented with their negative-CTE crystallographic z-axes parallel to
the plane of the honeycomb wall. A high degree of such orientation can be desirable
because it reduces the CTE of the honeycomb article in both the axial direction (within
the plane of the wall, parallel to the lengths of the channels) and radial direction
(within the plane of the wall, orthogonal to the lengths of the channels). The degree
of preferred crystal orientation is measured by x-ray diffractometry on a specimen
cut from the fired body. An "XRD I-ratio" is defined by the relation of EQ. 1
where I(110) and I(002) are the peak heights of the XRD reflections from the (110)
and (002) planes in the cordierite crystal lattice, based upon hexagonal indexing
of the XRD peaks, using copper Kα radiation. The "axial I-ratio," I
A, is measured by x-ray diffractometry on the axial cross section of the honeycomb,
that is, the cross section orthogonal to the length of the channels. The "transverse
I-ratio," I
T, is measured on the as-fired surface of the honeycomb wall, with the orthogonal walls
removed. The "powder I-ratio" is measured on powder prepared by pulverizing the honeycomb
specimen to a fine particle size. The value of the powder I-ratio also represents
the I-ratio for randomly oriented cordierite crystals and is about 0.655.
[0038] Near-random orientations are exemplified by cordierite crystallites in walls of the
honeycomb structure having a Δ
I ≤ 0.1 wherein Δ
I = I
T-I
A. In contrast, cordierite crystallites in walls of the low-microcracked honeycomb
structure of the disclosure which have a preferred orientation can have a Δ
I > 0.1. In embodiments, in porous ceramic honeycomb, the walls of the honeycomb structure
including a preferred orientation can have an I
A ≤ 0.60, an I
A ≤ 0.55, an I
A ≤ 0.50, or even an I
A ≤ 0.45. Furthermore, the walls of the honeycomb structure can have an I
T ≥ 0.70, an I
T ≥ 0.75, an I
T ≥ 0.80, or even an I
T ≥ 0.85. In embodiments, the low-microcracked honeycomb structures of the disclosure
which exhibit preferred orientation can have a Δ
I ≥ 0.2, a Δ
I ≥ 0.3, a Δ
I ≥ 0.4 or even a Δ
I ≥ 0.45.
[0039] To preserve good thermal shock resistance, the average coefficient of thermal expansion
of the cordierite ceramic honeycomb body over the 25°C-800°C (hereinafter the CTE)
should be relatively low. Accordingly, a CTE ≤ 18.0x10
-7/°C along at least one direction in the ceramic body may be exhibited in embodiments
of the disclosure. In embodiments, a CTE ≤ 16.0x10
-7/°C, or even a CTE ≤ 14.0x10
-7/°C along at least one direction are provided. In embodiments of the low-microcracked
honeycombs, the coefficient of thermal expansion of the cordierite ceramic honeycomb
body along at least one direction over the temperature range can have a CTE ≤ 12.0x10
-7/°C, or even a CTE ≤ 11.0x10
-7/°C. In embodiments, a CTE in the range of about 10.5x10
-7/°C to about 18.0x10
-7/°C can be provided, including for example a CTE in the range of from about 10.5 x10
-7/°C to about 14.0x10
-7/°C. In embodiments, a preferred orientation of the cordierite crystallites includes
having their z-axes parallel to the plane of the wall whereby Δ
I > 0.10, and a CTE ≤ 14.0x10
-7/°C. In embodiments a preferred orientation of the cordierite crystallites includes
having their z-axes parallel to the plane of the wall. In embodiments it is also preferred
that the CTE is at least 10.5x10
-7/°C because such CTE values are associated with a low degree of microcracking. For
this reason, it is further preferred that the CTE ≥ 12.0x10
-7/°C. In alternative embodiments where the orientation of the cordierite crystallites
within the wall is nearly random, such that Δ
I ≤ 0.10, the CTE can be from about 14.0x10
-7/°C to about 18.0x10
-7/°C.
[0040] The above values of CTE for the cordierite ceramic bodies can also be affected by,
for example, the degree of microcracking, the extent of crystallite orientation (microstructural
texturing) with respect to the plane of the wall or the extrusion direction, and the
amount of crystalline secondary phases such as spinel, sapphirine, mullite, and alumina
(corundum). Accordingly, it has been discovered that the degree to which the value
of CTE
25-800°C is reduced by microcracking, ΔCTE
mc, can be estimated by EQ. 2 or EQ. 3:
[0041] In EQ. 2 and EQ. 3, I
T and I
A are the transverse and axial XRD I-ratios, as defined above, %SCP is the total of
the weight percentages of the secondary crystalline phases in the fired ceramic body
as measured by powder x-ray diffractometry (XRD), equal to wt% spinel + wt% sapphirine
+ wt% mullite + wt% corundum; CTE
25-800°C is the measured coefficient of thermal expansion as defined above in units of 10
-7/°C; and ΔCTE
mc (I
T) and ΔCTE
mc (I
A) are in units of 10
-7/°C. Thus, for example, if the measured CTE
25-800°C is 12.0x10
-7/°C, a value of "12.0" is entered into EQ. 2 and EQ. 3. Likewise, for example, if
a value of "1.5" is computed from the right side of EQ. 2 or EQ. 3, it is meant that
the value of ΔCTE
mc (I
T) or ΔCTE
mc (I
A) is 1.5x10
-7/°C.
[0042] Larger (more positive) values of ΔCTE
mc (I
T) and ΔCTE
mc (I
A) indicate greater amounts of microcracking. Values of ΔCTE
mc (I
T) or ACTE
mc (I
A) that approach zero correspond to a lower degree of microcracking. In some embodiments,
the calculated value of ΔCTE
mc (I
T) or ΔCTE
mc (I
A) can even be slightly negative due to small contributions to CTE from other minor
factors or due to small errors in the measured values of the I-ratio, %SCP, or CTE
25-800°C. According to embodiments of the disclosure, the bodies can be characterized by a
value of ΔCTE
mc (I
T) or a value of ΔCTE
mc (I
A) that is less than 3.0x10
-7/°C, more preferably less than 2.0x10
-7/°C, less than 1.5x10
-7/°C, or even less than 1.0x10
-7/°C.
[0043] The microcrack parameter Nb
3 and the E-ratio E
900°C/E
25°C are measures of the level of microcracking in ceramic bodies, such as a cordierite
ceramics. We have discovered that for a low-microcracked cordierite body, the elastic
modulus gradually decreases with increasing temperature. This decrease in the elastic
modulus is believed to be attributable to the increasing distance between atoms within
the crystal structure with increasing temperature. An example of the decrease in elastic
modulus with increasing temperature for a porous, non-microcracked cordierite honeycomb
body is depicted in FIG. 1. FIG. 1 shows the elastic modulus versus temperature behavior
for a non-microcracked cordierite honeycomb ceramic during heating to 1,200°C (open
circles) and cooling back to room temperature (filled and open squares). The near
overlap of the heating and cooling trend lines signifies a virtual absence of microcracks.
The elastic modulus decrease has been found to be essentially linear from room temperature
to 900°C, or even to 1000°C. Above about 1,000°C, there is a greater rate of decrease
in elastic modulus with increasing temperature. This is believed to be due to the
softening, or even partial melting, of a small amount of residual glass phase that
originally formed by reaction of impurities or glass-forming metal oxide additions
during sintering of the ceramic. Surprisingly, the rate of change in the elastic modulus
with heating for a non-microcracked cordierite ceramic, ΔE°/ΔT, was found to be proportional
to the value of the elastic modulus of the non-microcracked body at room temperature,
E°
25°C, and is closely approximated by the relation of EQ. 4:
where the superscript "o" elastic modulus term (E
o) denotes the elastic modulus of the ceramic in a non-microcracked state. For non-microcracked
cordierite bodies, the temperature dependence of the elastic modulus during cooling
after heating to a high temperature, such as 1,200°C, is essentially identical to
the temperature dependence during the original heating, so that, at any given temperature,
the value of the elastic modulus during cooling is nearly the same as its value at
that temperature during heating. This is also illustrated in FIG. 1 for a low-microcracked
cordierite ceramic.
[0044] An example of the temperature dependence of the elastic modulus for a highly microcracked
cordierite ceramic body is displayed in FIG. 2. Thus, FIG. 2 shows the elastic modulus
versus temperature behavior for a microcracked cordierite honeycomb ceramic during
heating to 1,200°C (open circles) and cooling back to room temperature (filled and
open squares).
[0045] In a highly microcracked ceramic body, the elastic modulus increases gradually, and
then more steeply, with increasing temperature up to 1,200°C. This increase is believed
to be due to the re-closing, and eventual annealing, of the microcracks with heating,
so that the ceramic body has progressively fewer open microcracks at higher temperatures.
The increase in E due to the reduction in microcracking more than offsets the decrease
in E of the individual cordierite crystallites with heating, resulting in a more rigid
body at high temperature. As the ceramic is cooled from 1,200°C, the microcracks do
not immediately re-open, because micro-stresses are initially too low. As a result,
the trend in elastic modulus with cooling is initially that of a non-microcracked
cordierite body. The increase is steep at first due to the increase in viscosity of
any liquid or glass phase, possibly accompanied by a reduction in volume fraction
of the liquid or glass due to crystallization or devitrification, respectively. Between
about 1,000 and 700°C in the example in FIG. 2, the more gradual increase in E with
decreasing temperature can be ascribed to the natural increase in the elastic modulus
of the cordierite crystals with cooling. At temperatures below about 700°C, the elastic
modulus undergoes a gradual, then more rapid, decrease with cooling. This is due to
the progressive reopening of the microcracks and a decrease in the rigidity of the
ceramic. At room temperature, the elastic modulus has returned to a value close to
the initial value of the ceramic before the thermal cycle to 1,200°C.
[0046] The extent of microcracking in the cordierite ceramic is reflected in two features
of the elastic modulus heating and cooling curves. One manifestation of the degree
of microcracking is the extent to which the elastic modulus increases from 25°C to
900°C or to 1000°C during heating, as this increase is believed to be caused by a
re-closing of the microcracks. Based upon EQ. 4, one can calculate the ratio of the
elastic modulus of a non-microcracked cordierite body at 900°C or at 1,000°C to that
of a non-microcracked cordierite body at 25°C as being E
o900°C/E
o25°C = 1 + 875(-7.5x10
-5) = 0.934 or E
o100°C/E
o25°C = 1 + 975(-7.5x10
-5) = 0.927. These values of E
o900°C/E
o25°C and E
o1000°C/E
o25°C provide a baseline against which to compare the E
900°C/E
25°C and E
1000°C/E
25°C values of a microcracked ceramic body. For example, in FIG. 1, the ratio E
900°C/E
25°C is 0.95 and the ratio E
1000°C/E
25°C is 0.87, indicating a very low degree of microcracking. By contrast, in FIG. 2, the
ratio of E
900°C/E
25°C for the heating curve is 1.07 and E
1000°C/E
25°C is 1.12. These values are much higher than would be expected in the complete absence
of microcracking. Thus, the value of E
900°C/E
25°C or E
1000°C/E
25°C for a cordierite ceramic may be utilized as a quantitative measure of the extent
of microcracking in the room-temperature body. Thus, according to embodiments of the
disclosure E
900°C/E
25° ≤ 1.00, E
900°C/E
25°C ≤ 0.99, E
900°C/E
25°C ≤ 0.98, E
900°C/E
25°C ≤ 0.97, E
900°C/E
25°C ≤ 0.96, E
900°C/E
25°C ≤ 0.95, and even E
900°Cc/E
25°C ≤ 0.94. To that end, it should be noted that the minimum achievable value for E
900°C/E
25°C for a ceramic comprised of 100% cordierite is about 0.93 when the body is entirely
absent of microcracks. When a glass phase is also present in the cordierite ceramic
body, the value of E
900°C/E
25°C can be even less than 0.93 due to reduction in E
900°C by softening of the glass at high temperature.
[0047] Another indication of the degree of microcracking is the gap between the elastic
modulus heating and cooling curves. A method to quantify this hysteresis is based
upon the construction of a tangent to the cooling curve in a temperature region where
the sample is still in a non-microcracked state. In FIG. 2, such a tangent is shown
as line A-B, and the point of tangency is denoted by point "C". The slope of the tangent
line is, therefore, equivalent to the temperature dependence of the elastic modulus
of the non-microcracked cordierite body, as constrained by EQ. 4. Furthermore, the
value of this tangent line extrapolated back to room temperature (point A) is approximately
equivalent to the room-temperature elastic modulus of the sample if it were not microcracked
at room temperature, and is equal to E
o25°C for that sample. Thus, the equation of the tangent line is given by the following
general expression of EQ.5:
Where E
otangent denotes the elastic modulus of the non-microcracked body at each temperature, T,
along the tangent line.
[0048] An analytical method was devised for determining E
o25°C from the experimental measurements of the elastic modulus during cooling, after heating
to about 1,200°C. In accordance with this method, a second-order polynomial is fit
to the elastic modulus measurements made during cooling between about 1,000°C and
500°C, as a function of temperature (°C). This equation is of the following form:
[0049] The upper limit of the temperature range over which the experimentally measured elastic
modulus values are fit by EQ. 6 may be further restricted to a temperature less than
1000°C if it is determined that the trend in E versus temperature exhibits a very
high curvature at, or below, about 1000°C, due to, for example, the persistence of
substantial softening of a glass phase or formation of a small amount of liquid below
1,000°C. Likewise, the lower limit of the temperature range over which the experimentally
measured elastic modulus values are fit by EQ. 6 may be further restricted to a temperature
greater than 500°C if it is determined that the trend in E versus temperature exhibits
a very high curvature at, or above, about 500°C, due to, for example, substantial
reopening of the microcracks above 500°C. The method of least-squares regression analysis
is used to derive the values of the regression coefficients "a," "b," and "c" in EQ.
6. In FIG. 2, the polynomial fit to the open squares is represented by the solid curve
from 500 to 1,100°C.
[0050] The value of E
o25°C is obtained by solving for the elastic modulus and temperature at which the tangent
line, given by EQ. 5, intersects the polynomial curve fit to the elastic modulus data
during cooling, given by EQ. 6. The values of the elastic modulus and temperature
at this point of intersection are denoted E
i and T
i, respectively. In the example in FIG. 2, the values of E
i and T
i correspond to the triangle, point C. Because this point of intersection is common
to both the tangent line and the polynomial curve, it follows that
[0051] Also, at the point of tangency, the slope of the polynomial curve must equal that
of the tangent line. Therefore, it follows that
[0052] EQ. 7 and EQ. 8 provide two equations relating the two unknown quantities, E
o25°C and T
i, to one another. To solve for E
o25°C and T
i, EQ. 8 is first rearranged to yield
[0053] EQ. 9 is then substituted into EQ. 7 to give the following expression:
[0054] EQ. 10 may be rearranged to yield the following:
[0055] Gathering terms in EQ. 11 gives the following relation:
[0056] Further simplifying EQ. 12 yields
[0057] EQ. 13 may be re-expressed as
where C = {c-{b/(-7.5x10
-5)}{1 +7.5x10
-5(25)}}, B = {-2a/(-7.5x10
-5)}{1 +7.5x10
-5(25}}, and A = -a. The value of T
i can then be found by solving the quadratic formula:
[0058] EQ. 15 and EQ. 16 provide two possible values of T
i, of which only one will have a physically realistic value, that is, a value lying
between 25 and 1,200°C. The physically realistic value of T
i computed in this manner is then substituted into EQ. 9, from which the value of E
o25°C is calculated.
[0059] Once E
o25°C has been solved for, the ratio of the elastic modulus for the hypothetically non-microcracked
sample at 25°C, E
o25°C, to the actual measured value of the elastic modulus of the microcracked sample at
25°C, E
25°C is proportional to the degree of microcracking in the initial sample before heating.
That is, a greater degree of microcracking at room temperature will lower the value
of E
25°C, and thereby raise the value of E
o25°C/E
25°C.
[0061] Although based upon a number of simplifying assumptions, the quantity Nb
3, referred to herein as the "Microcrack Parameter," provides another useful means
to quantify the degree of microcracking in a ceramic body. For a non-microcracked
body, the value of Nb
3 is 0.00. In the example in FIG. 2, the value of Nb
3 is 0.184. In embodiments, it is therefore preferred that the value of Nb
3 be ≤ 0.08. In embodiments, it is more preferred for the ceramic honeycomb bodies
to exhibit microcrack parameters of Nb
3 ≤ 0.07, Nb
3 ≤ 0.06, Nb
3 ≤ 0.05, Nb
3 ≤ 0.04, Nb
3 ≤ 0.03, or even Nb
3 ≤ 0.02.
[0062] In preferred embodiments, the cordierite honeycomb body comprises a porosity of at
least 55%, a median pore diameter of not more than 5 microns, and a predicted thermal
shock limit, TSL, of at least 1100°C, and more preferably at least 1200°C. In these
embodiments, the ceramic honeycomb body further exhibits at least one of 1) a value
of E
900°C/E
25°C that is not more than about 0.95; 2) a value of the Microcrack Parameter, Nb
3, of not more than 0.02; and 3) a value of ΔCTE
mc (I
T) or ΔCTE
mc (I
A) that is not more than 2.0x10
-7/°C. Such an exemplary honeycomb body is well suited for use as a low-mass catalytic
converter substrate.
[0063] In other preferred embodiments, the ceramic honeycomb body has a porosity of at least
55%, a median pore diameter in the range of from 5 microns to 10 microns, and a predicted
thermal shock limit, TSL, of at least 1100°C, and more preferably at least 1200°C,
and even more preferably at least 1300°C, and further exhibits at least one of 1)
a value of E
900°C/E
25°C that is not more than about 0.95; 2) a value of the Microcrack Parameter, Nb
3, of not more than 0.02; and 3) a value of ΔCTE
mc (I
T) or ΔCTE
mc (I
A) is not more than 2.0x10
-7/°C. Such ceramic honeycomb bodies are well suited for use as diesel particulate filters
for very high filtration efficiency applications.
[0064] The bodies can be porous cordierite ceramic honeycomb bodies having a plurality of
cell channels extending between a first and second end as shown in Figs. 3 and 4,
for example. The ceramic honeycomb body may have a honeycomb structure that may be
suitable for use as, for example, flow-through catalyst substrates or wall-flow exhaust
gas particulate filters, such as diesel particulate filters. A typical porous ceramic
honeycomb flow-through substrate article 10 according to embodiments of the disclosure
is shown in Fig. 3 and includes a plurality of generally parallel cell channels 11
formed by and at least partially defined by intersecting cell walls 14 (otherwise
referred to as "webs") that extend from a first end 12 to a second end 13. The channels
11 are unplugged and flow through them is straight down the channel from first end
12 to second end 13. Preferably, the honeycomb article 10 also includes an extruded
smooth skin 15 formed about the honeycomb structure, although this is optional and
may be formed in later processing as an after applied skin. In embodiments, the wall
thickness of each cell wall 14 for the substrate can be, for example, between about
0.002 to about 0.010 inches (about 51 to about 254 µm). The cell density can be, for
example from about 300 to about 900 cells per square inch (cpsi). In a preferred implementation,
the cellular honeycomb structure can consist of multiplicity of parallel cell channels
11 of generally square cross section formed into a honeycomb structure. Alternatively,
other cross-sectional configurations may be used in the honeycomb structure as well,
including rectangular, round, oblong, triangular, octagonal, hexagonal, or combinations
thereof. "Honeycomb" refers to a connected structure of longitudinally-extending cells
formed of cell walls, having a generally repeating pattern therein.
[0065] Fig. 4 illustrates a honeycomb filter 100 in embodiments of the disclosure. The general
structure is the same as the flow-through substrate, including a body 101 made of
intersecting porous ceramic walls 106 extending from the first end 102 to the second
end 104. Certain cells are designated as inlet cells 108 and certain other cells are
designated as outlet cells 110. In the filter 100, certain selected channels include
plugs 112. Generally, the plugs are arranged at the ends of the channels and in some
defined pattern, such as the checkerboard patterns shown. The inlet channels 108 may
be plugged at the outlet end 104 and the outlet channels 110 may be plugged at the
inlet end 102. Other plugging patterns may be employed and all of the outermost peripheral
cells may be plugged (as shown) for additional strength. Alternately, some of the
cells may be plugged other than at the ends. In embodiments, some channels can be
flow-through channels and some can be plugged providing a so-called partial filtration
design. In embodiments, the wall thickness of each cell wall 14 for the filter can
be for example from about 0.006 to about 0.030 inches (about 152 to about 762 µm).
The cell density can be for example between 100 and 400 cells per square inch (cpsi).
[0066] References to cordierite ceramic bodies or honeycombs refer to cordierite composition
comprised predominately of Mg
2Al
4Si
5O
18. However, the cordierite bodies can also contain compositions of similar physical
properties, for example, "stuffed" cordierite compositions. Stuffed cordierites are
cordierites having molecules or elements such as H
2O, CO
2, Li, K, Na, Rb, Cs, Ca, Sr, Ba, Y, or a lanthanide element in the channel site of
the cordierite crystal lattice. Such constituents can impart modified properties,
such as improved sinterability or reduced lattice thermal expansion or thermal expansion
anisotropy, that may be useful for some applications. Also included are cordierites
having chemical substitutions of, for example, Fe, Mn, Co, Ni, Zn, Ga, Ge, or like
elements, for the basic cordierite constituents to provide, for example, improved
sinterability, color, electrical properties, catalytic properties, or like properties.
The symmetry of the crystal lattice of the cordierite phase can be, for example, orthorhombic,
hexagonal, or any mixture of phases having these two symmetries.
[0067] In embodiments, the disclosure also provides a method for making the porous cordierite
ceramic honeycomb structures described above, where a plasticized ceramic forming
precursor batch composition is provided by compounding an inorganic powder batch mixture
together with at least one glass forming metal oxide source; an organic binder; and
a liquid vehicle. The plasticized batch can further comprise one or more optional
constituents including pore-forming agents, plasticizers, and lubricants. The plasticized
batch is then formed by shaping, such as by extrusion, into a green honeycomb. These
green honeycombs are then dried, such as by microwave or RF drying, and fired in a
kiln to sinter or reaction-sinter the inorganic raw material sources into unitary
cordierite ceramic honeycomb bodies. The green bodies are fired for a time and at
a temperature sufficient to provide a sintered cordierite honeycomb including relatively
low microcracking and relatively high thermal shock resistance.
[0068] The inorganic powder batch can comprise a mixture of raw cordierite forming components
that can be heated under conditions effective to provide a primary sintered phase
cordierite composition. The raw cordierite forming batch components can include, for
example, a magnesium oxide source; an alumina source; and a silica source. As an example
the inorganic ceramic powder batch composition can be selected to provide a cordierite
composition consisting essentially of from about 49 to about 53 percent by weight
SiO
2, from about 33 to about 38 percent by weight Al
2O
3, and from about 12 to about 16 percent by weight MgO.
[0069] Exemplary magnesium oxide sources can include talc. In a further embodiment, suitable
talcs can comprise talc having a median particle size less than about 15 µm, or even
less than about 10 µm. Particle size is measured by, for example, a laser diffraction
technique, such as by a Microtrac® particle size analyzer. Examples of commercially
available magnesium oxide sources suitable for use in the present disclosure include,
Artic Mist Talc, available from Luzenac, Inc. of Oakville, Ontario, Canada, and 96-67
Talc available from Barrett's Minerals, Inc. of Dillon, Montana.
[0070] Exemplary alumina sources include alumina forming sources, which are chemical compounds
capable of forming aluminum oxide upon heating. Alumina forming sources include corundum
or alpha-alumina, gamma-alumina, transitional aluminas, aluminum hydroxide such as
gibbsite and bayerite, boehmite, diaspore, aluminum isopropoxide and the like. The
median particle size of the alumina source is preferably less than 8 µm, including
for example, median particle sizes less than 7 µm, less than 6 µm, less than 5, less
than 4, less than 3, less than 2, or even less than 1 µm. Commercially available alumina
sources can include relatively coarse aluminas, such as the Alcan C-700 series, having
a particle size of about 4-7 microns, and a specific surface area of about 0.5-1 m
2 /g,
e.g., C-701
™ and relatively fine aluminas having a particle size of about 0.5-4 microns, such
as A1000 SGD and A3000 available from Almatis.
[0071] If desired, the alumina source can include a dispersible alumina forming source.
A dispersible alumina forming source can be an alumina forming source that is at least
substantially dispersible in a solvent or liquid medium and that can be used to provide
a colloidal suspension in a solvent or liquid medium. In embodiments, a dispersible
alumina source can be a relatively high surface area alumina source having a specific
surface area of at least 20 m
2/g. Alternatively, a dispersible alumina source can have a specific surface area of
at least 50 m
2/g. In an exemplary embodiment, a suitable dispersible alumina source for use in the
methods of the disclosure includes alpha aluminum oxide hydroxide (lIOOH· xH
2O) commonly referred to as boehmite, pseudoboehmite, and as aluminum monohydrate.
In exemplary embodiments, the dispersible alumina source can include the so-called
transition or activated aluminas (
i.e., aluminum oxyhydroxide and chi, eta, rho, iota, kappa, gamma, delta, and theta alumina)
which can contain various amounts of chemically bound water or hydroxyl functionalities.
Specific examples of commercially available dispersible alumina sources that can be
used in the disclosure include Dispal 18N4-80, commercially available from Sasol North
America.
[0072] Suitable silica sources can include, for example, a clay or clays, such as raw kaolin,
calcined kaolin, or mixtures thereof. In embodiments, the silica source can preferably
have a median particle diameter less than 15 microns, or even more preferably less
than 10 microns. Exemplary clays include, for example, non-delaminated kaolin raw
clay, having a particle size of about 7-9 microns, and a surface area of about 5-7
m
2 /g, such as Hydrite MP
™ and those having a particle size of about 2-5 microns, and a surface area of about
10-14 m
2 /g, such as Hydrite PX
™ and delaminated kaolin having a particle size of about 1-3 microns, and a surface
area of about 13-17 m
2 /g, such as KAOPAQUE-10
™ or calcined clay, having a median particle size of about 1-3 microns, and a surface
area of about 6-8 m
2 /g, such as Glomax LL. All of the above named materials are available from Imerys
Minerals, Ltd. In embodiments of the disclosure, when kaolin or calcined kaolin is
present in the plasticized batch composition, the amount having a median particle
diameter less than about 7 microns is preferably less than about 5 percent by weight
of the inorganic raw materials, and is more preferably at least substantially absent
from the batch composition. It is further preferred that the raw material mixture
is absent of any kaolin or calcined kaolin.
[0073] In embodiments, the raw material mixture contains a silica forming source, by which
is meant a material comprising >95% SiO
2 or capable of converting to >95% SiO
2 during heating. The silica forming source can further include crystalline silica
such as quartz or cristobalite, non-crystalline silica such as fused silica or sol-gel
silica, silicone resin, zeolite, diatomaceous silica, and like materials. A commercially
available quartz silica forming source can include, for example, Imsil A25 Silica
available from Unimin Corporation. In embodiments, the silica forming source can include
a compound that forms free silica when heated, such as for example, silicic acid or
a silicon organo-metallic compound.
[0074] In addition to the raw cordierite forming batch components above, the inorganic powder
batch composition can also comprise one or more pre-reacted cordierite powders or
synthesized magnesium alumino-silicate glass powders. When cordierite powders or synthesized
magnesium alumino-silicate glass powders are selected for use in the batch, the particles
preferably have a median particle diameter of not more than 30 microns and a value
of (D
90-D
10)/D
50 of not more than 1.20. The values of D
10, D
50 (median particle diameter), and D
90 are the particle diameters of the powder at 10%, 50%, and 90% of the particle size
distribution, based upon particle volume, as measured by a laser diffraction technique.
[0075] Suitable pre-reacted cordierite compositions for use in the inorganic powder batch
can be obtained commercially from known sources, including for example, Corning Incorporated,
Corning, NY, USA. Alternatively, a suitable cordierite composition can also be manufactured
by heating a cordierite forming batch composition, as described above, under conditions
effective to convert the batch composition into a sintered phase cordierite. In embodiments,
a suitable pre-reacted cordierite consists essentially of from about 49 to about 53
percent by weight SiO
2, from about 33 to about 38 percent by weight Al
2O
3, and from about 12 to about 16 percent by weight MgO. For example, cordierite powders
suitable for the intended purpose can be obtained, for example, by the complete or
partial pre-reaction of inorganic precursor materials, including mineral combinations
such as clay + talc + alumina, spinel + silica, magnesia + alumina + silica, etc.,
or by the partial or complete devitrification (crystallization) of a magnesium alumino-silicate
glass frit; or by the partial or complete crystallization of a chemically precipitated
magnesium alumino-silicate material, such as a sol-gel powder. Alternatively naturally
occurring cordierites, ground to suitable particle sizes, can be used.
[0076] When the cordierite powder is prepared by reacting inorganic mineral raw materials
or chemically precipitated materials, it may be formed, for example, by fabricating
a mass of the mixed precursors or chemical precipitates, heating the mass to a temperature
sufficient to form cordierite, and then crushing the mass to the desired particle
size with optional sieving or air classification. Alternatively, the raw materials
or precipitates could also be pre-powdered by spheroidizing, such as by spray drying
or other atomization method, and the resulting granules heated to temperatures effective
to form cordierite. When the cordierite powder is prepared from a glass precursor,
the molten glass may be formed into a convenient shape and crushed, or it may be "drigaged"
by pouring the molten glass into a quenching liquid such as water. The resulting glass
feeds may then be ground to a desired particle size with optional sieving or air classification
to select an appropriately necessary particle size range.
[0077] In embodiments, the raw material mixture may further include at least one glass forming
metal oxide source. The glass forming metal oxide source can be a colloidal metal
oxide source that is capable of forming a colloidal suspension in a solvent and preferably
contains 0 to 97 wt% SiO
2, 0 to 97% MgO, 0 to 97% Al
2O
3, and at least 3.0 wt.% of one or more metal oxides selected from the group comprising
Li
2O, Na
2O, K
2O, CaO, Fe
2O
3, and TiO
2. The metal oxides can include, for example, at least 4%, at least 5%, or even at
least 6 wt.% of the colloidal metal oxide source. In embodiments, the colloidal metal
oxide source can include, for example, a colloidal silicate phase containing at least
50 wt% SiO
2 when the chemical formula is calculated on an anhydrous basis. The colloidal silicate
can be a colloidal phyllosilicate, such as attapulgite or bentonite clay. Still further,
in preferred embodiments, the glass forming metal oxide source can include a rare
earth element such as yttrium or lanthanum.
[0078] Other components that can be present in the batch compositions in relatively minor
proportions include, for example, oxides of impurity elements or intentional dopants
such as calcium, lithium, iron, titanium, sodium, potassium, boron, tungsten, bismuth,
and like elements. The ratio of magnesia, alumina, and silica components in the bulk
raw material mixture can be chosen to form only stoichiometric cordierite, or may
be selected to allow the formation of some spinel, sapphirine, mullite, forsterite,
enstatite, or a glass phase. In some embodiments, it is preferred that the sum of
Li + CaO + Na
2O + K
2O + and any rare earth oxide be at least 0.5 wt%.
[0079] The batch composition can include a pore-forming agent. The pore-forming agent can
include, for example, greater than or equal to 30%, 40%, 50%, or even 60% by weight,
of the inorganic raw materials by superaddition. The pore-forming agents can include,
for example, graphite, starch, or even combinations thereof. The starch can include,
for example corn, rice, or potato starch. In an example where a combination of graphite
and starch is employed, the pore-forming agents can include, for example greater than
or equal to 20% graphite and greater than or equal to 10% starch, as a superaddition
based upon 100% weight of the inorganic raw materials. In embodiments of the disclosure,
the pore former preferably has a median particle size diameter less than about 20
microns, less than about 15 microns, or even less than about 10 microns.
[0080] To provide the plasticized batch compositions of the disclosure, the inorganic powder
batch composition, including the aforementioned powdered ceramic materials, the glass
forming metal oxide source, and any pore former, can be compounded with a liquid vehicle,
an organic binder, and one or more optional forming or processing aids. Exemplary
processing aids or additives can include lubricants, surfactants, plasticizers, and
sintering aids. Exemplary lubricants can include hydrocarbon oil, tall oil, or sodium
stearate.
[0081] The organic binder component can include water soluble cellulose ether binders such
as methylcellulose, hydroxypropyl methylcellulose, methylcellulose derivatives, or
a combination thereof. Particularly preferred examples include methylcellulose and
hydroxypropyl methylcellulose. Preferably, the organic binder can be present in the
composition as a super addition in an amount in the range of from 0.1 weight percent
to 8.0 weight percent of the inorganic powder batch composition, and more preferably,
in an amount of from about 3 weight percent to about 6 weight percent of the inorganic
powder batch composition. The incorporation of the organic binder into the batch composition
can further contribute to the cohesion and plasticity of the composition. The improved
cohesion and plasticity can, for example, improve the ability to shape the mixture
into a honeycomb body.
[0082] A preferred liquid vehicle for providing a flowable or paste-like consistency to
the inventive compositions is water, although other liquid vehicles exhibiting solvent
action with respect to suitable temporary organic binders can be used. The amount
of the liquid vehicle component can vary in order to impart optimum handling properties
and compatibility with the other components in the ceramic batch mixture. Preferably,
the liquid vehicle content is present as a super addition in an amount in the range
of from 15% to 60% by weight of the inorganic powder batch composition, and more preferably
in the range of from 20% to 40% by weight of the inorganic powder batch composition.
Minimization of liquid components in the disclosed compositions can lead to further
reductions in undesired drying shrinkage and crack formation during the drying process.
[0083] In exemplary preferred embodiments, a batch composition of the disclosure can include,
for example, a mixture of a magnesium-containing source having a median particle diameter
of not more than about 15 microns, an alumina-forming source having a median particle
diameter of not more than about 8 microns, a silica-forming source having a median
particle diameter of not more than about 15 microns, a pore-forming agent having a
median particle diameter of not more than about 20 microns, and one or more metal
oxide sources whose presence increases the amount of glass phase in the fired body
whereby the total amount of Li
2O + Na
2O + K
2O + CaO + rare earth oxide in the fired body is at least about 0.5 weight percent.
The glass-forming metal oxide source is preferably a compound of a rare earth element
such as yttrium or lanthanum. Further, the amount of any kaolin or calcined kaolin
having a median particle diameter less than about 7 microns is less than about 5 percent
by weight of the inorganic raw materials, and is preferably absent from the batch.
[0084] In exemplary preferred embodiments, the batch composition can include, for example,
a mixture of a magnesium-containing source having a median particle diameter of not
more than about 15 microns, an alumina-forming source having a median particle diameter
of not more than about 8 microns, a silica-forming source having a median particle
diameter of not more than about 15 microns, a pore-forming agent having a median particle
diameter of not more than about 20 microns, and one or more metal oxide sources whose
presence increases the amount of glass phase in the fired body whereby the total amount
of Li
2O + Na
2O + K
2O + CaO + rare earth oxide in the fired body is at least about 0.5 weight percent.
The batch composition further comprises from about 0.001 to about 5 wt% of a pre-reacted
cordierite source or a magnesium alumino-silicate glass source. Once again, the glass-forming
metal oxide source is preferably a compound of a rare earth element such as yttrium,
or lanthanum. Still further, the amount of kaolin or calcined kaolin having a median
particle diameter less than about 7 microns is less than about 5 percent by weight
of the inorganic raw materials, and is preferably absent from the batch.
[0085] In exemplary preferred embodiments, the batch composition comprises a mixture of
about 5 to about 99 wt% of a pre-reacted cordierite source or a magnesium alumino-silicate
glass source having a median particle diameter of not more than about 30 microns and
a value of (D
90-D
10)/D
50 of not more than about 1.20. The batch composition also comprises a pore-forming
agent having a median particle diameter of not more than about 20 microns and one
or more components having a median particle diameter of not more than about 10 microns
selected from the group comprising a magnesia source, an alumina source, a silica
source; and a metal oxide source whose presence increases the amount of glass phase
in the fired body whereby the total amount of Li
2O + Na
2O + K
2O + CaO + rare earth oxide in the fired body is at least about 0.5 weight percent.
[0086] In preferred embodiments, the batch composition can include, for example, a mixture
of talc having a median particle diameter of not more than about 10 microns, an alumina-forming
source having a median particle diameter of not more than 8 microns, a silica-forming
source having a median particle diameter of not more than about 10 microns, and from
about 0.5 to about 3.0 weight percent of a Y
2O
3-forming source. Optionally, one or more pore-forming agents are also included having
a median particle diameter of not more than about 15 microns and being present in
a ratio of up to about 80 parts by weight pore-forming agent to about 100 parts by
weight inorganic raw materials.
[0087] The honeycomb substrate such as that depicted in FIG. 3 can be formed from the plasticized
batch according to any conventional process suitable for forming honeycomb monolith
bodies. For example, in embodiments a plasticized batch composition can be shaped
into a green body by any known conventional ceramic forming process, such as, e.g.,
extrusion, injection molding, slip casting, centrifugal casting, pressure casting,
dry pressing, and the like. In embodiments, extrusion can be done using a hydraulic
ram extrusion press, or a two stage de-airing single auger extruder, or a twin screw
mixer with a die assembly attached to the discharge end.
In the latter, the proper screw elements are chosen according to material and other
process conditions in order to build up sufficient pressure to force the batch material
through the die.
[0088] The resulting honeycomb body can then be dried, and subsequently fired under conditions
effective to convert the formed green composition into a primary sintered phase ceramic
composition. Conditions effective for drying the formed green body functionally can
include those conditions capable of removing at least substantially all of the liquid
vehicle present within the green composition. As used herein, at least substantially
all include the removal of at least about 95%, at least about 98%, at least about
99%, or even at least about 99.9 % of the liquid vehicle present prior to drying.
Exemplary and non-limiting drying conditions suitable for removing the liquid vehicle
include heating the green honeycomb substrate at a temperature of at least about 50°C,
at least about 60°C, at least about 70°C, at least about 80°C, at least about 90°C,
at least about 100°C, at least about 110°C, at least about 120°C, at least about 130°C,
at least about 140°C, or even at least about 150°C for a period of time sufficient
to at least substantially remove the liquid vehicle from the green composition. In
embodiments, the conditions effective to at least substantially remove the liquid
vehicle comprise heating the formed green body at a temperature of at least about
60°C. Further, the heating can be provided by any conventionally known method, including
for example, hot air drying, RF, microwave drying, or a combination thereof.
[0089] With reference again to FIG. 4, either before or after the green body has been fired,
a portion of the cells 110 of a formed monolithic honeycomb 100 can be plugged at
the inlet end 102 with a paste having the same or similar composition to that of the
body 101. The plugging is preferably performed only at the ends of the cells and form
plugs 112 having a depth of about 5 to 20 mm, although this can vary. A portion of
the cells on the outlet end 104 but not corresponding to those on the inlet end 102
may also be plugged in a similar pattern. Therefore, each cell is preferably plugged
only at one end. The preferred arrangement is to therefore have every other cell on
a given face plugged as in a checkered pattern as shown in FIG. 4. Further, the inlet
and outlet channels can be any desired shape. However, in the exemplified embodiment
shown in FIG. 4, the cell channels are square in cross-sectional shape.
[0090] The formed honeycomb bodies can then be fired under conditions effective to convert
the inorganic powder batch composition into a primary sintered phase cordierite composition.
Exemplary firing conditions can comprise heating the honeycomb green body at a maximum
firing temperature in the range of from about 1340°C to about 1435°C, and more preferably
in the range of from about 1375°C to about 1425°C, for a period of about 5 to about
30 hours.
[0092] To further illustrate the principles of the disclosure, the following examples provide
those of ordinary skill in the art with a complete disclosure and description of how
the cordierite honeycomb bodies and methods claimed herein are made and evaluated.
Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts,
temperatures, etc.); however, some errors and deviations may have occurred. Unless
indicated otherwise, parts are parts by weight, temperature is °C or is at ambient
temperature, and pressure is at or near atmospheric.
[0093] The disclosure is illustrated by non-limiting examples in the following tables. Table
1 provides the sources and median particle diameters of the raw materials used in
the examples as measured by a laser diffraction technique. Table 2 lists the parts
by weight of the raw materials used to make the inventive examples. Table 3 provides
the properties of inventive examples having substantial alignment of the cordierite
crystal z-axes within the plane of the honeycomb wall. Table 4 lists the properties
of inventive examples having nearly random cordierite crystal orientation within the
plane of the honeycomb walls.
[0094] In preparing the examples, inorganic raw materials and pore formers were mixed with
binders and lubricants, and water was added to the powder mixture in a stainless steel
muller to form a plasticized batch. The batch was extruded as 2-inch diameter honeycomb
having either approximately 300-325 cells/inch
2 and approximately 0.014-0.015-inch walls, or approximately 600 cells/inch
2 and approximately 0.004-inch walls. The extruded ware was dried and then fired in
an electrically heated kiln at the temperatures and hold times listed in the tables.
Heating rates were sufficient to prevent cracking of the ware and are well know in
the art. In the Tables, the mean coefficients of thermal expansion, in units of 10
-7/°C, were measured by dilatometry on a specimen parallel to the lengths of the channels
of the honeycomb article ("axial direction"). The %porosity is the volume percentage
of porosity in the walls of the article as measured by mercury porosimetry. The terms
d
1, d
2, d
5, d
10, d
25, d
50, d
75, d
90, d
95, d
98, and d
99 denote the pore diameters, in microns, or micrometers (10
-6 meters), at which 1%, 2%, 5%, 10%, 25%, 50%, 75%, 90%, 95%, 98%, and 99% of the total
pore volume are of a finer pore diameter, respectively, also as measured by mercury
porosimetry. Thus, for example, d
90 is the pore diameter at which 90% (by volume) of the pores have a smaller diameter
(equal to the pore diameter at which the cumulative mercury intrusion volume equals
10% of the total mercury intrusion volume). It therefore follows that, for example,
d
10 < d
50 < d
90.
[0095] Weight percentages of residual mullite, spinel + sapphirine, and alpha-alumina in
the fired samples were measured by x-ray diffractometry. The amount of spinel and
sapphirine are included together due to the potential difficulty in distinguishing
between the two phases, depending upon the XRD technique used.
[0096] The axial XRD I-ratio and transverse XRD I-ratio are defined by EQ. 1 and were measured
by x-ray diffractometry using copper Kα radiation. For randomly oriented cordierite
crystals, the axial and transverse I-ratios are both equal to approximately 0.655.
[0097] All modulus of rupture (MOR), or flexural strength, values were measured by the four-point
method on a cellular bar (½ inch x ¼ inch x 2.75 inches long) parallel to the axial
direction of the honeycomb. MOR data in the tables typically represent the averaged
measurements on four to six bars. Elastic modulus values were measured by a sonic
resonance technique also on a cellular bar (1 inch x ½ inch x 5 inches long) parallel
to the axial direction. The thermal shock parameter, TSP, was computed as described
previously from (MOR
25°C/E
25°C)(CTE
500-900°C)
-1, and thermal shock limit, TSL, is defined as TSP + 500°C. Also computed were the
thermal shock parameter, TSP*, defined as (MOR
25°C/E
25°C)(CTE
200-1000°C)
-1, and the thermal shock limit, TSL*, defined as TSP* + 200°C. The value of TSL* is
thus an estimate of the maximum temperature to which the cordierite body will survive
without fracture when the coolest region of the body is at 200°C.
[0098] The closed frontal area, CFA, of the honeycomb is the area fraction of the face of
the honeycomb comprised of the porous ceramic walls, and is computed as wN{2(N
-0.5) -w}, where w is the wall thickness and N is the cell density (cells per unit area).
The value of MOR/CFA is therefore an estimate of the MOR of the porous ceramic comprising
the wall of the honeycomb.
[0099]
Table 1. Raw material sources and median particle sizes
Raw Material |
Supplier |
Product Code |
D50 (microns) |
Talc A |
Luzenac |
Artic Mist |
5.0 |
Talc B |
Barretts Minerals |
96-67 |
14 |
Alumina A |
Almatis |
A1000 SGD |
0.6 |
Alumina B |
Almatis |
A3000 |
3.4 |
Alumina C |
Alcan |
C701 |
6.8 |
Boehmite |
Sasol North America Inc. |
Dispal 18N4-80 |
0.12 |
Kaolin A |
IMERYS Minerals Ltd. |
Kaopaque K10 |
3.0 |
Calcined Kaolin B |
IMERYS Minerals Ltd. |
Glomax LL |
3.0 |
Quartz A |
Unimin Corporation |
Imsil A25 |
4.5 |
Cordierite Powder A |
Corning |
- |
4.4 |
Cordierite Powder B (1) |
Corning |
- |
23 |
Yttrium Oxide |
H.C. Starck, GmbH |
Grade C |
0.8 |
Magnesium Silicate Smectite Clay (2) |
Southern Clay Products, Inc. |
Laponite® RD |
0.025 |
Attapulgite (3) |
Active Minerals Co. LLC |
Acti-Gel® 208 |
2.0 µm x 3 nm |
Bentonite (4) |
Wyo-Ben, Inc. |
Big Horn@ CH325 |
-325 mesh |
Graphite A |
Asbury Carbons |
4602 |
35 |
Graphite B |
Asbury Carbons |
4014 |
9.3 |
Graphite C |
Asbury Carbons |
Micro 450 |
5.8 |
Rice Starch |
American Key Food Products LLC |
Remy Rice Starch |
7.1 |
Corn Starch |
National Starch & Chemical Co. |
National@ 465 |
16 |
Methyl Cellulose |
The Dow Chemical Co. |
METHOCEL™ F240 |
- |
Hydrogenated Dimeric 1-Decene |
Innovene USA LLC |
Durasyn® 162 |
- |
Stearic Acid |
Cognis Corp. |
Emersol 120 |
- |
Sodium Stearate |
Witco Corp. |
- |
- |
Tall Oil Fatty Acid |
S and S Chemical Co. |
L-5 |
- |
(1) (D90 - D10)/D50 = 1.03
(2) Contains approximately 3 wt% Na2O and 1 wt% Li2O
(3) Contains approximately 3 wt% Fe2O3 and 1.9 wt% CaO
(4) Contains approximately 3.5 wt% Fe2O3, 2.3 wt% Na2O, and 0.4 wt% CaO |
[0100]
Table 2. Batch compositions of inventive examples
Batch Number |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
Talc A |
42.24 |
42.24 |
42.24 |
42.24 |
42.24 |
42.24 |
42.24 |
42.38 |
42.38 |
- |
Alumina A |
- |
- |
29.35 |
29.35 |
- |
29.35 |
29.35 |
- |
- |
- |
Alumina B |
- |
29.35 |
- |
- |
- |
- |
- |
- |
- |
- |
Alumina C |
29.35 |
- |
- |
- |
29.35 |
- |
- |
30.12 |
30.12 |
- |
Boehmite |
6.00 |
6.00 |
6.00 |
6.00 |
6.00 |
6.00 |
6.00 |
5.00 |
5.00 |
1.79 |
Kaolin A |
- |
- |
- |
- |
- |
- |
- |
- |
- |
3.94 |
Quartz A |
22.41 |
22.41 |
22.41 |
22.41 |
22.41 |
22.41 |
22.41 |
23.50 |
23.50 |
- |
Cordierite Powder A |
- |
- |
- |
- |
- |
- |
- |
1.00 |
1.00 |
- |
Cordierite Powder B |
- |
- |
- |
- |
- |
- |
- |
- |
- |
90.00 |
Yttrium Oxide |
1.00 |
1.00 |
1.00 |
1.00 |
1.00 |
1.00 |
1.00 |
- |
- |
- |
Mg Silicate Smectite |
|
|
|
|
|
|
|
|
|
|
Clay |
- |
- |
- |
- |
- |
- |
- |
- |
- |
4.27 |
Attapulgite |
- |
- |
- |
- |
- |
- |
- |
5.00 |
- |
- |
Bentonite |
- |
- |
- |
- |
5.00 |
5.00 |
- |
- |
5.00 |
- |
Graphite A |
- |
- |
- |
- |
- |
- |
- |
45.00 |
45.00 |
15.00 |
Graphite B |
45.00 |
45.00 |
45.00 |
20.00 |
- |
- |
35.00 |
- |
- |
- |
Graphite C |
- |
- |
- |
- |
45.00 |
45.00 |
- |
- |
- |
- |
Rice Starch |
15.00 |
15.00 |
15.00 |
20.00 |
15.00 |
15.00 |
20.00 |
- |
- |
- |
Corn Starch |
- |
- |
- |
- |
- |
- |
- |
15.00 |
15.00 |
10.00 |
Methyl Cellulose |
5.00 |
5.00 |
5.00 |
6.00 |
5.00 |
5.00 |
6.00 |
6.00 |
6.00 |
8.00 |
Durasyn 162 |
6.00 |
6.00 |
6.00 |
4.60 |
6.00 |
6.00 |
4.60 |
- |
- |
- |
Stearic Acid |
0.60 |
0.60 |
0.60 |
- |
0.60 |
0.60 |
- |
- |
- |
- |
Sodium Stearate |
- |
- |
- |
- |
- |
- |
- |
1.00 |
1.00 |
1.00 |
Tall Oil |
- |
- |
- |
0.60 |
- |
- |
0.60 |
- |
- |
- |
Table 3. Properties of examples having substantially non-random crystal orientation
Example Number |
4.1 |
4.2 |
4.3 |
4.4 |
4.5 |
4.6 |
4.7 |
4.8 |
Batch Number |
1 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
Tmax (°C) |
1380 |
1360 |
1380 |
1380 |
1380 |
1380 |
1380 |
1380 |
Hold Time (hours) |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
Pore Volume (ml/g) |
0.7910 |
0.8097 |
0.7065 |
0.6534 |
0.5151 |
0.6466 |
0.5907 |
0.5958 |
%Porosity |
66.8 |
65.8 |
62.6 |
60.1 |
56.9 |
62.0 |
60.8 |
59.7 |
d1 |
2.8 |
3.6 |
1.7 |
1.5 |
1.2 |
3.4 |
1.5 |
1.2 |
d2 |
3.6 |
4.3 |
2.2 |
1.7 |
1.4 |
4.1 |
1.8 |
1.5 |
d5 |
4.9 |
5.4 |
2.9 |
2.0 |
1.8 |
5.0 |
2.1 |
1.9 |
d10 |
6.0 |
6.4 |
3.4 |
2.3 |
2.0 |
5.9 |
2.3 |
2.2 |
d25 |
8.0 |
7.9 |
4.2 |
2.7 |
2.4 |
7.7 |
2.6 |
2.6 |
d50 |
10.0 |
9.4 |
5.2 |
3.1 |
2.7 |
9.3 |
3.0 |
3.0 |
d75 |
12.6 |
11.9 |
6.5 |
3.5 |
3.2 |
11.3 |
3.6 |
3.5 |
d90 |
30.8 |
35.6 |
11.6 |
4.7 |
4.7 |
21.3 |
5.0 |
4.8 |
d95 |
98.4 |
117.4 |
44.0 |
8.6 |
8.2 |
56.7 |
8.5 |
8.7 |
d98 |
204.1 |
206.7 |
155.2 |
18.8 |
14.0 |
142.1 |
17.6 |
16.1 |
d99 |
260.6 |
253.9 |
210.6 |
38.4 |
21.2 |
202.4 |
33.2 |
27.8 |
(d50-d10)/d50 = df |
0.40 |
0.32 |
0.35 |
0.26 |
0.26 |
0.37 |
0.24 |
0.26 |
(d90-d50)/d50 = dc |
2.08 |
2.78 |
1.22 |
0.50 |
0.71 |
1.28 |
0.69 |
0.63 |
(d90-d10)/d50 = db |
2.48 |
3.10 |
1.57 |
0.76 |
0.97 |
1.65 |
0.92 |
0.89 |
CTE (25-800) 10-7/°C |
13.0 |
12.5 |
13.2 |
12.0 |
12.0 |
13.2 |
12.5 |
10.8 |
CTE (500-900) 10-7/°C |
19.8 |
19.4 |
19.4 |
19.2 |
18.8 |
19.9 |
19.5 |
17.9 |
CTE (200-1000) 10-7/°C |
17.0 |
16.7 |
17.1 |
16.7 |
16.4 |
17.5 |
17.0 |
15.4 |
ΔCTEmc based on IT (10- 7/°C) |
0.9 |
1.7 |
0.4 |
1.4 |
0.5 |
0.3 |
0.2 |
1.5 |
ΔCTEmc based on IA (10- 7/°C) |
1.1 |
2.4 |
0.6 |
1.3 |
-0.3 |
0.2 |
0.1 |
1.0 |
Axial I-ratio, IA |
0.48 |
0.52 |
0.48 |
0.46 |
0.41 |
0.47 |
0.44 |
0.41 |
Transverse I-ratio, IT |
0.82 |
0.80 |
0.82 |
0.83 |
0.86 |
0.82 |
0.85 |
0.87 |
% Mullite |
0.8 |
0 |
0 |
0 |
0 |
0.6 |
0.9 |
0 |
% Spinel + Sapphirine |
1.6 |
1.7 |
1.6 |
1.7 |
1.4 |
0.7 |
0.5 |
1.6 |
% Alumina |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
Cell Density (inches-2) |
600 |
600 |
600 |
600 |
600 |
600 |
600 |
600 |
Wall Thickness (10-3 inches) |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
Closed Frontal Area Fraction (CFA) |
0.186 |
0.186 |
0.186 |
0.186 |
0.186 |
0.186 |
0.186 |
0.186 |
MOR (psi) |
197 |
145 |
297 |
409 |
410 |
431 |
442 |
330 |
MOR/CFA (psi) |
1059 |
780 |
1597 |
2199 |
2202 |
2320 |
2376 |
1774 |
E at 25°C (105 psi) |
1.12 |
0.935 |
1.81 |
2.79 |
4.58 |
2.25 |
3.02 |
2.60 |
E at 900°C (105 psi) |
1.04 |
0.892 |
1.68 |
2.64 |
- |
- |
- |
- |
E at 1000°C (105 psi) |
0.948 |
0.812 |
1.54 |
2.42 |
- |
- |
- |
- |
E(900°C)/E(25°C) |
0.93 |
0.95 |
0.93 |
0.95 |
- |
- |
- |
- |
E(1000°C)/E(25°C) |
0.85 |
0.87 |
0.85 |
0.87 |
- |
- |
- |
- |
Microcrack Parameter, Nb3 |
0.008 |
0.015 |
0.014 |
0.017 |
- |
- |
- |
- |
MOR/E |
0.176% |
0.156% |
0.164% |
0.147% |
0.089% |
0.192% |
0.146% |
0.127% |
TSP = (MOR/E)25°C(CTE500-900°C)-1 |
889 |
801 |
844 |
762 |
475 |
966 |
750 |
708 |
TSL = TSP + 500 |
1389 |
1301 |
1344 |
1262 |
975 |
1466 |
1250 |
1208 |
TSP* = (MOR/E)25°C(CTE200-1000°C)-1 |
1034 |
934 |
957 |
880 |
547 |
1099 |
860 |
824 |
TSL* = TSP* + 200 |
1234 |
1134 |
1157 |
1080 |
747 |
1299 |
1060 |
1024 |
Table 4. Properties of examples having near-random crystal orientation
Example Number |
5.1 |
5.2 |
5.3 |
Batch Number |
8 |
9 |
10 |
Tmax (°C) |
1380 |
1380 |
1340 |
Hold Time (h) |
20 |
20 |
15 |
Pore Volume (ml/g) |
0.5383 |
0.5471 |
0.4454 |
%Porosity |
56.5 |
57.2 |
52.5 |
d1 |
1.0 |
1.4 |
1.6 |
d2 |
2.0 |
2.1 |
2.1 |
d5 |
3.5 |
3.4 |
3.1 |
d10 |
4.8 |
4.6 |
4.1 |
d25 |
6.9 |
6.5 |
6.2 |
d50 |
8.5 |
8.2 |
7.9 |
d75 |
9.6 |
9.3 |
9.2 |
d90 |
13.1 |
13.0 |
11.7 |
d95 |
49.7 |
49.0 |
26.0 |
d98 |
171.8 |
164.9 |
118.4 |
d99 |
229.3 |
221.0 |
205.6 |
(d50-d10)/d50 = df |
0.43 |
0.44 |
0.48 |
(d90-d50)/d50 = dc |
0.54 |
0.59 |
0.48 |
(d90-d10)/d50 = db |
0.97 |
1.03 |
0.95 |
CTE, 25-800 (10-7/°C) |
14.5 |
14.7 |
15.8 |
CTE, 500-900 (10-7/°C) |
21.0 |
22.1 |
22.4 |
CTE, 200-1000 (10-7/°C) |
18.6 |
19.5 |
20.1 |
ΔCTEmc based on IT (10- 7/°C) |
2.6 |
2.4 |
2.2 |
ΔCTEmc based on IA (10- 7/°C) |
2.5 |
2.3 |
3.3 |
Axial I-ratio, IA |
0.61 |
0.61 |
0.64 |
Transverse I-ratio, IT |
0.68 |
0.68 |
0.66 |
% Mullite |
0 |
0.5 |
1.2 |
% Spinel + Sapphirine |
1.3 |
0.8 |
0.7 |
% Alumina |
0 |
0 |
0 |
Cell Density (inches-2) |
325 |
325 |
300 |
Wall Thickness (10-3 inches) |
15 |
15 |
14 |
Closed Frontal Area Fraction |
0.47 |
0.47 |
0.43 |
MOR (psi) |
972 |
972 |
640 |
MOR/CFA (psi) |
2068 |
2068 |
1488 |
E at 25°C (105 psi) |
9.04 |
9.33 |
6.29 |
E at 900°C (105 psi) |
8.39 |
- |
6.34 |
E at 1000°C (105 psi) |
8.13 |
- |
6.33 |
E(900°C)/E(25°C) |
0.928 |
- |
1.008 |
E(1000°C)/E(25°C) |
0.899 |
- |
1.006 |
Microcrack Parameter, Nb3 |
0.003 |
- |
0.065 |
MOR/E |
0.107% |
0.104% |
0.102% |
TSP = (MOR/E)25°C(CTE500-900°C)-1 |
512 |
471 |
454 |
TSL = TSP + 500 |
1012 |
971 |
954 |
TSP* = (MOR/E)25°C(CTE200-1000°C)-1 |
579 |
534 |
507 |
TSL* = TSP* + 200 |
779 |
734 |
707 |
[0101] The inventive examples in Table 3 illustrate honeycomb bodies made with fine talc,
alumina, and fine silica raw materials with 1.0 wt% Y
2O
3 addition, with addition of pore-forming agents, and lacking a kaolin source. Such
combinations yield a low degree of microcracking, high porosity, fine pore size, and
a thermal shock parameter, TSP, of at least 450°C. Furthermore, the absence of a cordierite
powder or magnesium alumino-silicate glass in the raw material mixture results in
a ceramic body in which the cordierite crystallites exhibit a high degree of orientation
with their z-axes parallel to the plane of the honeycomb wall, as indicated by the
low values of the axial XRD I-ratio less than 0.60 and high values of the transverse
XRD I-ratio greater than 0.70. Consequently, the CTE
25-800°C values range from only 10.8x10
-7/°C to 13.2x10
-7/°C. The low degree of microcracking in Example 4.4 is illustrated by the near absence
of hysteresis between the elastic modulus heating and cooling curves in FIG. 1. The
benefit of a high porosity in providing high strain tolerance, (MOR/E)
25°C, in the inventive examples is shown in FIG. 5.
[0102] The inventive Examples 5.1 and 5.2 of Table 4 demonstrate honeycomb bodies made with
the addition of 1 wt% of a pre-reacted cordierite powder of fine particle size (4.4
microns) to mixtures of talc, alumina-forming sources, and quartz with pore-forming
agents and impure colloidal clays that contribute one or more of sodium, calcium,
and iron to the ceramic body to increase the amount of glass phase in the fired body.
The use of a pre-reacted cordierite powder results in fired bodies that substantially
lack preferred orientation of the cordierite crystallites and which exhibit an axial
XRD I-ratio greater than 0.60 and a transverse XRD I-ratio less than 0.70 and a CTE
25-800°C of at least 14x10
-7/°C. Examples 5.1 and 5.2 possess a low degree of microcracking, high porosity, fine
pore size, and a thermal shock parameter, TSP, of at least 450°C. Example 5.3 was
made from 90 wt% of a pre-reacted cordierite powder with addition of fine boehmite,
kaolin, and a colloidal clay to serve as an inorganic binder phase, and pore-forming
agents to increase porosity. The colloidal smectite clay also contributes sodium and
lithium impurities to increase the amount of glass phase in the fired body. Because
the particle size of the pre-reacted cordierite powder is finer than about 30 microns,
the fired body possesses a low degree of microcracking. Also, because the particle
size distribution of the cordierite powder is narrow as indicated by the value of
(D
90 - D
10)/D
50 < 1.20, and because the median particle diameters of the pore-forming agents are
closely matched to that of the cordierite powder, the final pore size distribution
is relatively narrow. The narrow pore size distribution and high porosity result in
a ratio of MOR/E of about 0.10% and a TSP of 454°C.
[0103] Applicant has found that addition of a pore former to conventional raw material mixtures
that contain a fine kaolin and lack a rare earth oxide addition or the addition of
another glass-forming metal oxide source is sufficient to increase porosity, for example,
to > 50%, but does not produce a body having a low degree of microcracking and high
strain tolerance.
[0104] The disclosure has been described with reference to various specific embodiments
and techniques. However, many variations and modifications are possible while remaining
within the spirit and scope of the disclosure.
[0105] In an additional embodiment, the porous ceramic honeycomb body, comprises:
a primary cordierite ceramic phase having:
a median pore size diameter d50 of from about 5 to about 10 microns;
an Eratio less than or equal to 0.95, where Eratio is E900°C / E25°C and E900°C is the Young's elastic modulus at 900°C and E25°C is the Young's elastic modulus at 25°C;
a thermal shock parameter (TSP) of at least 450°C, where TSP is (MOR25°C/E25°C)(CTE500-900°C)-1, MOR25°C is the modulus of rupture strength at 25°C, and CTE500-900°C is a high temperature thermal expansion coefficient measured at from about 500°C
to about 900°C; and
ΔCTEmc(IA) less than or equal to 2.0 x 10-7/°C.
[0106] In an exemplary method for making a porous ceramic honeycomb body, the method comprises:
providing a plasticized ceramic forming precursor batch composition, comprising:
an inorganic powder batch mixture comprising a magnesium source having a median particle
size diameter D50 less than or equal to 15 microns, an alumina forming source having a median particle
size diameter D50 less than or equal to 8.0 microns, and a silica forming source having a median particle
size diameter D50 less than or equal to 15 microns;
at least 0.5 wt% of at least one glass forming metal oxide source;
an organic binder; and
a liquid vehicle;
forming a honeycomb green body from the plasticized cordierite precursor batch composition;
and
firing the honeycomb green body to form a porous ceramic honeycomb body comprising
a primary cordierite ceramic phase having a median pore size diameter d50 less than 7.9 microns; an elastic modulus ratio E900°C/E25°C of not greater than 1.01; and a thermal shock parameter (TSP) of at least 450°C;
where TSP is (MOR25°C/E25°C)(CTE500-900°C)-1, MOR25°C is the modulus of rupture strength at 25°C, E25°C is the Young's elastic modulus at 25°C, E900°C is the elastic modulus at 900°C measured during heating, and CTE500-900°C is the high temperature thermal expansion coefficient at from about 500°C to about
900°C.
[0107] The exemplary method, optionally wherein the at least one glass forming metal oxide
source comprises an yttrium source, a lanthanum source, or a combination thereof.
[0108] The exemplary method, optionally wherein the at least one glass forming metal oxide
source comprises a source of calcium, potassium, sodium, lithium, iron, or combinations
thereof.
[0109] The exemplary method, optionally wherein the plasticized ceramic forming precursor
batch composition further comprises a pre-reacted cordierite powder or a magnesium
alumino silicate glass powder.
[0110] The exemplary method, optionally wherein the plasticized ceramic forming precursor
batch composition further comprises a particulate pore forming agent having a median
particle size diameter D
50 less than or equal to 20 microns.
[0111] The exemplary method, optionally wherein the plasticized ceramic forming precursor
batch composition, comprises:
an inorganic powder batch mixture comprising talc having a median particle size diameter
D50 less than or equal to 10 microns, an alumina forming source having a median particle
size diameter D50 less than or equal to 8 microns, and a silica forming source having a median particle
size diameter D50 less than or equal to 10 microns;
at least 0.5 wt.% of a glass forming yttrium oxide source; and
an optional particulate pore forming agent having a median particle size diameter
D50 less than or equal to 15 microns.